1. Field of the Invention
The present invention relates to a wafer carrier, a wafer conveying system, a stocker, and a method of replacing gas.
2. Background Art
The present invention typically relates to a sealed-type wafer carrier for accommodating and carrying wafers in the manufacture of semiconductor devices, and to stocking and conveying of the wafer carrier. The present invention will be described below exemplifying the case of the manufacture of a semiconductor device.
FIG. 8 is a perspective view for illustrating a known wafer carrier of a side-door integrated type used at the time of manufacturing the semiconductor device, and FIG. 9 is a perspective view illustrating an inside of the door of the wafer carrier. FIG. 10 is a sectional view illustrating the wafer carrier placed on a table of a wafer processing apparatus and accommodating wafers.
Wafer carriers include, for example, a wafer carrier described in a catalog made by FLUOROWARE Company. This type of wafer carrier is referred to as FOUP in the SEMI Standards. A conventional wafer carrier will be described below exemplifying an FOUP.
FOUP is the abbreviation of a “Front Opening Unified Pod”. Detailed information, such as dimensions, is described in the SEMI Standards E 52, E 1.9, or E 47.1.
In FIG. 8, reference numeral 100 denotes a wafer carrier, and the wafer carrier 100 has a carrier shell 10 and a carrier door 20. The carrier shell 10 is a housing having an open face in one surface, and the carrier door 20 fits to the carrier shell 10 at this open face. In the state where the carrier door 20 fits to the carrier shell 10, that is, in the state where the carrier door 20 is closed, the wafer carrier 100 is in a sealed state.
As FIG. 9 shows, a sealing material (packing) 21 is provided on the surface where the carrier door 20 contacts the carrier shell 10. This sealing material (packing) 21 is provided so as to maintain air-tightness between the carrier door 20 and the carrier shell 10.
Wafers are accommodated in the above-described wafer carrier 100, and conveyed automatically, for example, with an automatic transfer system called an OHT (overhead hoist transport) together with the wafer carrier 100 to a wafer processing apparatus that performs required processing.
In general, the wafer processing apparatus is installed in a room known as a clean room where temperature and humidity are controlled, and dust is eliminated. Therefore, the wafers are also conveyed in this clean room.
The reason why wafers are accommodated in an airtight carrier, and conveyed and processed in a clean room is to protect the wafers from foreign matter in the atmosphere and chemical contamination.
The carrier shell 10 and the carrier door 20 of the wafer carrier 100 are generally formed of a high-performance plastic material. However, plastic materials have a property to permeate moisture or the like. Thus, even if the wafer carrier 100 is in a sealed state, moisture or the like may enter inside the wafer carrier 100.
On the other hand, the atmospheric air may permeate into the wafer carrier 100 from the sealing material (packing) 21 used for maintaining the air-tightness of the wafer carrier 100 due to molecular diffusion or the like.
Therefore, the humidity, oxygen content, or the like in the wafer carrier 100 tend to increase with the lapse of time.
Also, when wafers whereto a photoresist is applied are stocked in the wafer carrier 100, the organic solvent vaporized from the photoresist applied to the wafers may adhere to the internal wall of the wafer carrier 100. In this case, even after the wafers whereto the photoresist is applied are removed, the organic solvent adhered to the internal wall of the wafer carrier 100 may remain intact. Thereafter, by the re-vaporization of the organic solvent, the atmosphere inside the water carrier 100 may be contaminated by organic compounds.
As a measure against such elevations of humidity and oxygen content, and organic contamination in a wafer carrier 100, there has been proposed a method of introducing N2 or dry air from the bottom of the wafer carrier 100 to replace the atmosphere inside the wafer carrier 100.
However, as FIG. 10 shows, a plurality of wafers 40 are horizontally accommodated in the wafer carrier 100. If N2 gas is simply introduced from the bottom of the wafer carrier 100 in this state, wafers 40 or the like accommodated in the wafer carrier 100 interfere with N2 gas to diffuse throughout the wafer carrier 100.
When the atmosphere inside the wafer carrier 100 is replaced, N2 gas for replacement is usually introduced from the bottom of the wafer carrier 100. This is due to ease of the placement of piping required for flowing the gas for replacement and discharging the inside atmosphere. However, when the gas for replacement is introduced from the bottom, it is feared that foreign matter deposited on the bottom may be blown up.
As described above, even if the wafer carrier is airtight, outside air or moisture permeates due to the characteristics of plastics or rubber, and humidity or oxygen content inside the wafer carrier may increase. Also, by accommodating wafers whereto a photoresist is applied are stocked, the atmosphere inside the wafer carrier may be contaminated by organic compounds.
Even if N2 gas or dry air is simply introduced into the wafer carrier to solve the problems above, obstructs in the wafer carrier, such as wafers, make it difficult to replace the atmosphere inside the wafer carrier with a clean gas in a short time.
Furthermore, when N2 gas or dry air is introduced from the bottom of the wafer carrier, foreign matter deposited on the bottom may be blown up to contaminate the atmosphere inside the wafer carrier.
However, the elevation of humidity or oxygen content in the wafer carrier, or the contamination of the wafer carrier by the organic solvent and foreign matter raises problems of the growth of natural oxide films, and poor gate oxide integrity.
Therefore, in order to solve these problems, an object of the present invention is to provide a wafer carrier, a wafer conveying system, a stocker, and a method of replacing gas that can replace the atmosphere inside the wafer carrier efficiently in a short time while preventing the mixing of foreign matter.